At the ng-conf event in May 2016 there were sessions discussing how Angular 2 can support server side rendering in various platforms. If you're working on a project running on Node.js, then Angular 2 is a native citizen. For other options like ASP, Java and PHP there are a few options on the table.

[...] Later during the ng-conf more details on the Server Side Rendering (Universal Rendering in Angular lingo) can be implemented in different environments to improve first page load experience. [...] The downside of these approaches is that you need to add additional complexity either by adding a dependency to an external service or require a rather exotic PHP extension at this point.

Instead he suggests using Twig along with the Angular 2 template compiler and some custom extensions to the base templating to format the output as Angular is expecting it. He talks about how the current backend rendering of templates could easily be translated to this handling. He also suggests that even just partial server-side rendering might be enough to help with the performance of the application.

As is mentioned in this new post on the Symfony Finland site, the functionality allowing the Twig templating engine to perform Angular 2 Universal Rendering.

Angular is a household name when it comes to JavaScript frameworks. They've been going through a major transition since the announcement of Angular 2. In the latest development Angular 2 will be getting PHP / Twig support for isomorphic rendering.

[...] So the Angular and the Drupal development teams have started working together to bring Universal Rendering to PHP and Twig. The details remain murky on how exactly this will be implemented (using a Node.js server or a PHP library), but a PHP library (not an extension written in C) would be the easiest option for developers.

He points out that there's also a chance that the result could be coupled to Drupal (at least at first) but hopes are that it will end up as a generic component usable in any system using Twig. The post also includes links where you can find out more information about the topic of "Isomorphic Rendering" too.